Cattle on straw cut nitrogen losses

Ammonia emissions from livestock not only pollute the environment but also increase farmers’ costs through reduced nitrogen availability in their manure and slurry, according to experts at the Institute of Grassland and Environmental Research at a recent open day.

More than half the ammonia emissions from farming came from cattle, with 26% originating in housing and 29% released during slurry spreading.

However, by bedding stock on straw rather than in scraped cubicle systems, farmers could cut housing emissions by over 40%, said IGER’s Sarah Gilhespy.

And the more straw used, the lower the emissions.

“We housed 12 cattle in four polytunnels and bedded them at a rate of 3.5kg of straw per head a day, plus 33%, 66% and 100%.

“We then measured ammonia emissions twice a week from October to April and discovered that increasing straw use reduced ammonia emissions.”

Doubling straw use cut emissions by more than 40%, but the most cost-effective bedding rate to reduce emissions was 4.7kg a head, she added.

In the storage phase, it was slurry which came out on top, producing less ammonia than manure due to the formation of a crust.

Manure heaps lost nutrients both through leaching and gaseous escape – and anyone composting manure was losing even more ammonia at the turning stage, said Nadine Loick.

“However, you can reduce nitrogen and potassium losses by covering the heap, from about 40% and 35%, respectively, to around 25% and 15% over a six-month period.”

Composting also improved soil structure, reduced weeds and pathogens and halved the volume of manure to be spread, she added.

And it was in spreading slurry and manure that many farmers lost out, due to inaccurate spreading rates and inappropriate machinery, said senior research officer John Laws.

“There’s no point reducing losses from housing and storage when you let it all go to waste at application.”